Currently, sheets such as bills are printed in many countries in the world. As one of techniques for preventing counterfeiting of securities such as bills, there is a printing technique using a magnetic ink.
Also, there is a technique for reading magnetic properties of securities printed using the printing technique using a magnetic ink.
Magnetic detecting devices for reading magnetic properties of sheets such as securities detect magnetic properties of the sheets, in a state of being installed in various apparatuses. For example, the magnetic detecting devices are installed in sheet processing apparatuses for determining the authenticity of bills, and detect magnetic properties of the bills.
In sheet processing apparatuses, for example, a large number of electrical devices such as an alternating-current motor used to generate rotational power or circulate air and a power supply transformer used to generate a direct-current voltage from an alternating-current voltage are arranged.
These electrical devices discharge magnetic noise out of the electrical devices based on the operation principles.
Accordingly, magnetic sensing units in magnetic detecting devices installed in the sheet processing apparatus may detect a surrounding environmental magnetic field such as magnetism generated by the electrical devices, as well as detecting magnetic properties of sheets. In this case, the magnetic detecting devices cannot precisely detect magnetic properties of sheets.